Systems for capturing energy from wind, known as wind energy systems, are known in the art and comprise a vertical mast with its bottom end fixed to the ground, the seabed or a floating platform and a nacelle mounted to turn about a vertical axis on a portion of the top end of the mast. The rotary portion of the system is mounted on the nacelle to rotate about an axis that is substantially horizontal or slightly inclined to the horizontal and comprises a hub and two or more blades fixed to the hub and extending radially therefrom relative to the rotation axis of the hub. The hub rotates on the nacelle in one or more bearings. Electricity is produced from wind energy captured by the rotary portion of the system by a generator such as an alternator which can include one or more stators secured to the nacelle and one or more rotors secured to the hub of the rotary portion of the system.
One problem encountered by manufacturers of wind energy systems is the need to obtain a high electrical power rating at the same time as limiting the size of the electricity generator, which impacts on the size of the nacelle. It is known in the art that disk generators, i.e. machines comprising one or more rotors and one or more stators with facing annular faces on which there are disposed magnetic or electromagnetic members that cooperate to produce electricity, can be advantageous because a relatively large active surface area of the machine can be obtained within a small volume. These systems are particularly advantageous if the rotor of the generator is fixed directly to the rotary portion of the system, thereby avoiding the need to use a mechanical speed multiplier.
However, this technique has not been routinely used on an industrial scale until now because it is difficult to design a rotary mounting for the rotary portion and the rotor such that it is possible block and/or balance forces, in particular axial forces, exerted on the rotary portion in order to maintain the position of the rotor or rotors relative to the stator disks.
The rotary portion of the wind energy system is subjected to forces exerted by the wind, which in particular cause flexing of the hub and its rotary support means, even if one or more thrust bearings are provided to compensate axial forces exerted on the rotary portion.
If the rotor of the generator is fixed to the rotary portion of the wind energy system, the forces exerted by the wind on the rotary portion are transmitted directly to the rotor of the generator, and it is then difficult in a disk machine having one or more rotor disks facing one or more stator disks to maintain the width of the airgaps of the generator at values that are small and precise.
Also, when the wind energy system is operating, the rotary portion of the system, and especially the rotor, is subjected to alternating forces and deformations that lead to fatigue failure of these components in service.
Also known in the art are systems for producing electricity from wind energy comprising a conventional radial flux alternator whose rotary portion rotates on the nacelle in a bearing such as a rolling bearing fixed to a tubular shaft secured to the nacelle and having an axis slightly inclined to the horizontal. The hub of the rotary portion of the system is secured to a tubular support which rotates on the outer race of the bearing and which carries the radial rotor of the electricity generator on a portion at its end opposite the hub carrying the blades. In this case the wind exerts a force via the blades and the hub that tends to cause the rotor to pivot relative to the bearing of the rotary portion about an axis perpendicular to the axis of the bearing.
The hub carrying the blades of the rotor, which are fixed cantilever-fashion relative to the bearing, exerts high levels of torque on the bearing and on the support structure of the wind energy system.
Because very high performance permanent magnets are now available off the shelf, producing disk electricity generators including a rotor carrying permanent magnets can now be envisaged, and disk machine rotors and stators can be made that limit the weight and the total length of the electricity generators.
It is therefore highly advantageous to be able to produce a wind energy system with a structure enabling a permanent magnet disk electricity generator to be used.